The first part of this investigation is a study of the platelet response to gram-negative septicemia (E. coli). It attempts to answer 5 questions: 1) What are the serial changes with sepsis in the number of circulating platelets and their functional and morphologic characteristics? 2) Are the observed changes similar in animals who die and those who survive the experimental period? 3) Are the platelet responses the gram-negative sepsis similar in newborn compared to the more mature experimental subject? 4) What is the mechanism of the progressive thrombocytopenia that develops with gram-negative sepsis? 5) Does the platelet response play a significant role in the pathophysiology of gram-negative shock? Newborn and maturing piglets are studied. Platelet count, platelet aggregation to ADP, number of circulating aggregates and electron microscopic appearance of platelet pellets are all serially determined. Light and electron microscopic examination of tissue sections at autopsy are done. The bone marrow of septic and control animals are compared and the number of megakaryocytes counted. The second part of this investigation compares the responses and survival of animals subject to 3 different forms of peritonitis: 1) anaerobic gram-negative bacilli (Bacteroides fragilis fragilis) plus sterile feces, 2) aerobic gram-negative bacillis (E. Coli) plus sterile feces, and 3) anaerobic gram-negative bacillis (Bacteroides fragilis fragilis plus aerobic gram-negative bacillis (E. Coli) plus sterile feces. Serial quantitative blood cultures, pH and arterial blood gases, cardiac output, pulse rate, blood pressure, Hct, total protein, white blood cell count, white blood cell function and serum insulin and sugar are measured. BIBLIOGRAPHIC REFERENCES: Rowe, M.I., Arango, A.: The Neonatal Response to a Massive Dose of Methylprednisolone. Journal of Pediatric Surgery. Vol. 11, No. 6, December, 1976. Rowe, M.I., Poole, A. Catherine: Clinical Evidence of Intestinal Absorption of Gastrografin. Radiology 118: 151-153, January, 1976.